The present invention relates to electromagnetic projectile launchers and particularly to an improved electromagnetic launcher which is driven by a single phase alternator with superconducting excitation.
Heretofore, electromagnetic projectile launchers have generally utilized a source of high DC current which is applied to a pair of parallel, elongated current rails. A projectile is equipped with brushes which make sliding electrical contact with these rails. The flow path of this high DC current conducted between the rails by these brushes and the attendant magnetic fields can be made to interact in ways well known in the art to develop tremendous accelerating forces propelling the projectile along the rails to desired high exit velocities. Alternatively, the projectile may be equipped with an insulating sabot designed to set up plasma arcs for conducting the DC current between the rails. Typical sources of the high DC current are homopolar or acyclic generators and capacitor banks. U.S. Pat. Nos. 4,423,662; 4,437,383; 4,449,441; 4,480,523; 4,485,720; and 4,555,972 are representative disclosures of homopolar generator driven electromagnetic launchers.
One of the principal objectives of any electromagnetic launcher design is the achievement of a desirably high projectile exit or muzzle velocity consistent with a reasonable rail or barrel length. It will be appreciated that if the barrel is too long, it can not be readily slewed to follow a moving target. To achieve a barrel of reasonably slewable length, acceleration of the projectile through the barrel must be increased. Since acceleration is proportional to the square of the current, this means that the current must be increased. However, any projectile has a limit to the magnitude of accelerating forces it can withstand. Peak acceleration and thus peak current must therefore be held below the accelerating force withstand limits of the projectile. Consequently, the acceleration profile over the barrel length should be reasonably flat such that the ratio of average acceleration to peak acceleration approaches unity. Thus, the current should have as close to a square pulse waveform as possible in order to achieve the desired exit velocity in the shortest possible barrel length. Homopolar generators have been found to be the most practical source of such a high magnitude, essentially square current pulse.
There is however a very significant problem engendered by this essentially square current pulse. At the moment the projectile exits the muzzle, the current is still at a very high level. Tremendous energy is thus stored in the inductances of the rails and the generator. The result is violant arcing between the rails, together with an intense flash which is easily detectable from a considerable distance. This so-called "muzzle blast" causes erosion and thermal damage to the muzzle ends of the rails. As evidenced by the above-cited U.S. Pat. Nos. 4,423,662 and 4,437,383, it has been proposed to permanently connect an impedance across the muzzle ends of the rails and into which the arcing current occasioned by the exiting projectile is commutated. Muzzle arcing is thus suppessed.
For these reasons, in an article entitled "A Compulsator Driven Rapid-Fire EM Gun" appearing in IEEE Transactions on Magnetics, Vol. Mag.-20, Mar. 1984, co-authored by the applicant herein, it was proposed to use an iron core single phase pulsed alternator to drive an electromagnetic launcher. The purpose of utilizing an AC waveshape was to increase launcher efficiency and reduce muzzle blast by timing the projectile exit at the muzzle to occur just prior to the naturally occurring current zero to facilitate interruption. The problem with this approach was twofold: a) the poor form factor of the current waveshape increased barrel length for a specified projectile muzzle velocity and peak acceleration; and b) the mass of the all iron system was excessive for practical kinetic energy weapons and other further applications. While this article recognizes the possibility of increasing muzzle velocity by initiating the discharge earlier at a different voltage firing angle, the penalty of lower launcher efficiency and the re-introduction of muzzle flash was considered unacceptable.
It is accordingly an object of the present invention to provide an improved electromagnetic launching system.
A further object is to provide an electromagnetic launching system of the above character which is driven by a single phase, pulse rated, alternating current generator with superconducting excitation.
Another object of the present invention is to provide an electromagnetic launching system of the above-character, wherein the magnitude of residual energy in the launching system at the time of projectile exit is reduced.
Yet another object is to provide an electromagnetic launching system of the above-character wherein high exit velocities are achievable while maintaining the barrel at a reasonable length.
A still further object is to provide an electromagnetic launching system of the above-character wherein muzzle blast is effectively and efficiently suppressed.
Other objects of the invention will in part be obvious and in part appear hereinafter.